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Hollow chisel mortiser setup

I recently purchased the Delta 14-651 hollow chisel mortiser for a bed I am building. I started putting 1/2" square holes just over 1' deep in one of the pieces last night and noticed that the bit got quite hot after only a couple of holes. I am wondering if I have it set up properly or if that is to be expected in hard wood such as the read oak I am using.

The center drill bit that came with the machine has a center point, a scoring point on the outside edge and a planing/scraping point/surface to clean the bottom of the hole. I apologize if I am not using the proper terms but I hope the description is adequate. The manual seems to indicate that the planing/scraping point/surface should be between 1/16 and 3/16 below the tips of the square chisel that surrounds the bit. I have it adjusted to about the middle of that range. This leaves the center point and the scoring point quite a bit below the chisel points. Does that sound about right.

I also notice that I have to pull down pretty hard on the handle. It is quite big and beefy but I never like forcing things. Any tips are appreciated.

(post #105256, reply #1 of 16)

The clearance for the bit is about right. I found with my chisels that it really helped to polish the outsides (flats) with fine sandpaper on a piece of glass and a little oil . I polished out all the machining marks and that made a big difference. Now they cut white oak very smoothly.

(post #105256, reply #2 of 16)

I did as Larry advised and it makes a difference. One more thing to consider is clamping the piece down. Without noticing, your left hand is pushing the wood into the bit causing deflection. And take it easy on the lever, I've snapped two of the pins so far!

(post #105256, reply #4 of 16)

I have the same HCM and first used it to make a large kitchen table from hard maple.

I used the 1/2" chisel and had eight mortises to make. I, too, noticed the chisel getting hot and noticed that around the fourth mortice, the handle required alot more downward force.

I later learned that a good set of chisels (in the sizes that came with your HCM) can rival the cost of the machine.

I also learned that cheaper chisels (like those that came with your HCM) lose their edge rather quickly. I ordered two cone shaped grinders that you chuck up in your drill. One is 50d the other 51d. The 51d puts a bevel on the edge.. and then you work the flats on a stone or sand paper.

Once the chisels are sharpened in this fashion the entire operation goes a whole lot more smoothly.

As to the distance your bit should protrude from the chisel.. the Delta operator manual for this tool is easy to understand and gets you right where you need to be.

I'm glad I got the machine. It beats the heck out of hogging out a mortice with a drill bit and squaring up with chisels.

(post #105256, reply #5 of 16)

Consider the square chisel part as if it really is a chisel. Don't expect it to cut well out of the box. Sharpen the sides like you would the back side of a chisel, and use the conical sharpeners to get the inside.

(post #105256, reply #6 of 16)

Thanks for all the tips. Sharpening the chisels makes sense - I was amazed at the difference a few minutes of sharpening made on my new out of the box Stanley low angle block plane. I think I can handle sharpening the outside of the hollow chisel bit but what do people use for the inside? I am not familiar with the conical shapers or the 50d and 51d stone grinders. Are there any recommended sources?Thanks again.Chris

(post #105256, reply #15 of 16)

That'll teach me to check more carefully.I saw the page with the mortising attachment,but only read"this product is discontinued" and moved on to sharpening.And I thought I knew the catalogue inside out.LOL.

(post #105256, reply #8 of 16)

While it may cut against your personal grain, you do have to lean on these tools a bit to get an efficient cut. If you pull too slowly, the bit doesn't roll up the wood in strands: it grinds it up into powder. When this happens, it's harder to clear the chips/powder, and the whole assembly builds up heat. This will cause you to wear the chisel bezel down more rapidly.

The trick is having your chisels sharp, a stout hold-down for the wood, and a steady, somewhat rapid pull on the handle. I usually pull down slowly until the bit has just started to cut into the wood, and the chisels have just made contact. Then I stroke the entire cut in less than a second.

Most folks use a penny or a dime to set the extension of the bit. Here's one way. Loosen up the chisel housing slightly and the loosen the bit all of the way. Slip a penny into the gap between the chisel housing and the mortiser. Take a piece of wood and lift it up to the bit/chisel until the chisel is up tight against the penny and the housing. Tighten the drill bit. Now the chisel point and the drill bit are at the same depth. Pull the penny out and slide the chisel housing up all of the way. Tighten it. This gives you an appropriate and consistent gap. It's easier to do than explain.

(post #105256, reply #9 of 16)

Try spraying teflon (I believe the stuff I have is made by Elmers) on the sides of the chisle and into the openings on the chisle sides that expose the bit. This provides lubrication for both the chisle and the bit during the cut. It probably cools them down as well. I do this at the start of each mortice. I can definitely tell the difference when I forget to use the spray. The spray is pretty inert and doesn't stain the wood at all. I'd like to say I was brilliant and came up with the idea, but it came from the manager of the store where I bought the tool.

The only other suggestion might be in the pattern of making the plunges. If it takes five passes, for example to complete the mortice, do the passes on the end, middle and other end first. This leaves the last two passes with openings on both sides for chips to escape. I started using the approach because experience with smaller chisle sizes. I could make an accurate cut into a fresh piece, but if I had made a plunge next to a previous cut, the force on the sides of the chisle were unequal and the chisle would wander a little. I was also concerned about what the torquing was doing to the bit inside, but I never broke one. With the pattern suggested, every cut has equal force on the two opposing sides. The chip removal benefit just comes with it.